The present invention relates generally to a fuel-valve, and more particularly, the present invention relates to a fuel valve that maintains fuel pressure in a fuel rail.
Modular reservoir assemblies (MRAs), also known as fuel pump modules or simply as senders are devices positioned in a vehicle fuel tank assembly used to supply fuel to the engine and provide other functions such as measuring fuel level and tank pressure. MRAs contain a check valve designed primarily to maintain fuel system pressure and to keep fuel from draining from the fuel rail and fuel injectors back to the tank after the engine and fuel pump is shut down. Maintaining pressure in the fuel rail and injectors is especially important when the engine is hot to keep the fuel from boiling. If the fuel boils, vapor bubbles form in the fuel rail and injectors, thereby making the engine difficult to start.
During the normal cooling cycle of the fuel system, a small vacuum is often created in the fuel rail and injectors due to differential thermal contraction of the fuel. Since the check valve will open under vacuum and allow fuel to flow into the fuel rail, the amount of vacuum produced is limited by the opening pressure of the check valve. Modern check valves (such as Forward Flow Check Valves-FFCVs) have higher opening pressures than most older fuel pump (or MRA) check valves because they incorporate a return spring to help keep the valve closed. Older design check valves use a lighter spring or no spring at all, instead relying only on gravity to close the check valve. The much higher opening pressure of the new FFCVs leads to much higher vacuums in fuel delivery components, such as MRA, the filter, fuel lines, fuel rail, fuel pressure regulator and fuel injectors. This excess vacuum may damage components not designed for vacuum, and has been observed to cause small air leaks which allow air to leak into the MRA, lines, the fuel rail, injectors, regulator or other components designed only to resist pressure, but not necessarily to resist vacuum. In addition, even if no air leaks occur, under certain conditions or with certain gasoline, vacuum within the fuel system has the potential of causing air/vapor bubbles from an air leak or air dissolved in the fuel to form from a gas leak and air dissolved in the fuel.
The problem with air intrusion from fuel delivery components or air/vapor bubble formation from the fuel is that it degrades fuel system performance by slowing down the pressurization of the fuel rail. The present invention was developed in light of these and other drawbacks.
To address these and other drawbacks, the present invention provides a fuel system that utilizes a first valve assembly and a second valve assembly. Preferably, the first valve assembly is in parallel with the second valve assembly and provides a greater bias against fuel flow from the fuel tank assembly to the fuel rail or to the environment should the external line leak. The second valve assembly allows fuel flow from the fuel tank assembly to the fuel rail and is set at a lower bias than that for the first valve assembly. Additionally, the second valve assembly allows a lower fuel flow rate from the fuel tank assembly to the fuel lines and rail than does the first valve assembly.
Other aspects of the invention will be apparent to those skilled in the art after reviewing the drawings and the detailed description below.